The present invention relates to an optical pickup device and an optical disc apparatus.
JP-A-2006-344344, page 26, FIGS. 3 and 5, has disclosed this technical field as background art. This document discloses as an objective that “a desirable signal is obtained with high accuracy from an optical disc having a plurality of recording layers.” As solving means to achieve the above-mentioned objective, the document discloses that “the optical beam of a P-polarized light emitted from an optical source unit (51) is reflected by an optical disc (15) to be turned into an S-polarized light and incident on a lens (61). At ¼ wavelength plates (62, 63), an optical phase difference of +¼ wavelength is added to the optical beam incident on +X side of an optical axis, and the optical phase difference of −¼ wavelength is given to the optical beam incident on −X side, respectively. In this way, signal light passed through the ¼ wavelength plate (63) is turned into the S-polarized light, stray light is turned into the P-polarized light, and a polarization optical device (64) transmits the signal light alone.” Further, the Technical Report of IEICE CPM2005-149 (2005-10), page 33, FIGS. 4 and 5, has disclosed as a problem that “a reflected light from one layer different from a targeted layer and a stray light from the other layer are incident on a photodetector to occur an offset in a TE signal when recording/reproducing a dual layer disc. Accordingly, in the case of the existing configuration without having a stray light provision against other layers, the offset of the TE signal on the dual layer disc becomes large compared with the case of a single layer disc, so that a stable control cannot be obtained.” As solving means to eliminate the above-mentioned problem, this document discloses that “a tracking photodetector is arranged on a domain on which the stray light does not occur by the other layer.” The configuration of the above description has also been disclosed in JP-A-2004-281026, page 71, FIGS. 22, 24 and 25.